Seismic surveys are extensively used in the oil and gas industry to understand the subsurface and to provide structural images of the geological formation within the earth using reflected sound waves. The results of the survey are used to identify reservoir size, shape and depth as well as porosity and the existence of fluids. Geophysicists and geologists use this information to pinpoint the most likely locations for successfully drilling for oil and natural gas.
A seismic survey may be conducted by placing a large number of geophones in the area of interest. The geophones may be set up in lines or in grids. Using shakers, rams, or small explosives, the ground is shaken and the geophones acquire the reflected sound data from the different sub-layers in the ground. Another method, the so-called “micro seismic” survey, uses passive measurement of natural or secondary disturbances to create a picture of the sub-surface structure. A huge amount of data is collected in a given seismic survey which may cover 40 sq km and take days to gather.
The amount of data which is retrieved during a seismic survey is quite large. In an exemplary case a geophone measures three axes at a sampling rate of 4 bytes per millisecond (each byte is 8 bits giving a resolution of 24 bits which is the accuracy required by the seismic survey). In this case, the data rate per geophone is 4 bytes/msec×8 bits/byte×3=96 kbps (Kilobits per second).
If the survey is using 1000 geophones, the data rate is then 96 Mbps (Mega bits per second). Because wireless systems have overhead and error correction to operate reliably, even the highest data rate broadband wireless systems can't accommodate this data rate in traditional configurations such as point to multipoint or pure mesh systems.
Several patent documents are known that use wireless links in a seismic network, including U.S. Pat. Nos. 6,424,931; 6,041,283; 6,219,620; and 7,224,642, and PCT Patent Publication No. WO 2009129601. However, there is room for improvement in the manner in which data is collected and delivered for processing.